THIS IS A RUSH TRANSCRIPT. THIS COPY MAY NOT BE IN ITS FINAL FORM AND MAY BE UPDATED.

MILES O'BRIEN, CNN ANCHOR: Thirty-nine miles up, add more than 12,000 miles per hour, a routine re-entry becomes a national tragedy. (BEGIN VIDEO CLIP)

GEORGE W. BUSH, PRESIDENT OF THE UNITED STATES: This day has brought terrible news.

UNIDENTIFIED FEMALE: The walls started shaking. A thunderous noise booming in what seem to be right in our backyard.

UNIDENTIFIED MALE: We lost the data and that's when we clearly begun to know that we had a bad day.

BUSH: The Columbia is lost. There are no survivors.

UNIDENTIFIED MALE: Sort of sad and sorry for the families of people that have been lost.

(END VIDEO CLIP)

ANNOUNCER: This tonight, from the launch to the last minutes of Columbia's ill-fated return trip, what NASA and the astronauts knew.

(BEGIN VIDEO CLIP)

UNIDENTIFIED MALE: That impact was on the left wing. We can't discount -- discount that there might be a connection.

(END VIDEO CLIP)

ANNOUNCER: This is a CNN Special Report: Columbia: A Shuttle Tragedy.

O'BRIEN: You are looking at a live picture, Nacogdoches, Texas, where debris from the Space Shuttle Columbia waits to be collected and analyzed.

Good evening, from CNN world headquarters in Atlanta. I'm Miles O'Brien.

For Americans who lived through Challenger, or the Apollo fire, the feelings are all too familiar, disbelief, shock and grief.

Once again we are reduced to looking at pictures, over and over, and asking ourselves how could this have happened? And once again, we are learning the names of extraordinary people, seven of them, whose lives were filled with knowledge, accomplishments, and daring.

We're learning about them, but now, we will never get to know them. For the second time in NASA's history, a space shuttle has been lost along with its entire crew. The Shuttle Columbia streaking home after a 16-day mission, suddenly crumbled, broke apart, and burned up just minutes before its scheduled touchdown. It was a scene that horrified the nation, much of the world.

During the next hour we're going to tell you as much as we can about what happened early this morning in the bright blue, big sky over the state of Texas.

To report on this tragedy and the investigation we will be joined by CNN's Wolf Blitzer, at the Johnson Space Center near Houston, Texas; Lou Dobbs at the Kennedy Space Center in Florida. And if you are just joining us or have been away from our coverage for a time, we begin with my colleague Anderson Cooper who will summarize the latest developments -- Anderson.

ANDERSON COOPER, CNN ANCHOR: Thank you, Miles.

New information continues to come in to CNN regarding today's shuttle disaster. Human remains have been recovered in Hemphill, Texas. Authorities presume it is one of the astronauts, pending positive ID. There are no reports anyone on the ground was injured by falling debris.

The remaining shuttles, Atlantis, Discovery and Endeavour have been grounded for the foreseeable future. The next shuttle flight had been set for March 1, no longer.

One problem NASA will have to address, in the meantime, is how to resupply the crew aboard the International Space Station. There is no immediate danger. They have enough food and supplies to last them through the end of May.

And President Bush returned to the White House from Camp David soon after learning this morning's tragic news. A short time later he made a televised address to the nation and ordered flags at government sites lowered to half staff, that will last through Wednesday.

The president said that despite the painful loss the U.S. space programs would continue.

Those are the latest developments at this hour, now our special coverage continues with Miles O'Brien.

O'BRIEN: Thank you, Anderson.

Columbia's mission came to an abrupt and catastrophic end, literally over the heads of NASA controller in Houston, Texas. And that is where we find CNN's Wolf Blitzer this evening -- Wolf.

WOLF BLITZER, CNN ANCHOR: Miles, the words were very chilling. The words, the last communication that we heard, Mission Control here, at the Johnson Space Center, in communication with the Space Shuttle Columbia, the seven members of the crew.

Let's listen to the final exchange between the crew and Mission Control.

(BEGIN AUDIO TAPE)

UNIDENTIFIED MALE: And, Columbia, Houston: We see your tire pressure messages, and we did not copy your last.

UNIDENTIFIED MALE: Roger...

(END VIDEO CLIP)

BLITZER: That was it. That was the last exchange between the Mission Control at the Johnson Space Center, where I am right now, and the members of the crew of the Space Shuttle Columbia.

The next thing, within a few minutes, white streaks were seen flashing across the skies over Texas. Streaks containing debris, scaring a lot of people, of course. They heard a tumultuous explosion, a loud boom, and then the next thing they knew, debris raining on parts of Texas, raining all across Texas. Indeed all the way over to Louisiana, perhaps as far away as other states as well.

CNN's Ed Lavandera is joining us now from Nacogdoches, Texas, where there has been some extensive debris already spotted -- Ed.

ED LAVANDERA, CNN CORRESPONDENT: Well, Wolf, if you can imagine this morning, as many north Texas and east Texas residents were waking up this morning, they had heard word that they would be able to get a chance to see the space shuttle streaking, it's plume streaking across the Texas sky, which is a bright blue color this morning, as it was headed toward Florida.

Many people watching it live on television here today, this morning, getting that rare chance to see the space shuttle streak toward Florida. And many people got to see live, what had happened, the catastrophic ending the Space Shuttle Columbia's mission.

And if you can imagine, just from the southeast point of Dallas, imagine a cone shape spreading out from across east Texas and even parts of Louisiana, we now understand, a debris field that is massive for investigators to have to comb through and search through.

They have warned people to stay away from the debris. We are here at a parking lot in downtown Nacogdoches, Texas, where there is about a three-foot piece of debris, which has become a gathering point here for people to come by and reflect as to what has happened here today.

But this scene has played out all over east Texas as many people have experienced debris falling near their homes, and that sort of thing. We understand that there has been a huge effort to collect all of this, or at least to begin the process of containing that wreckage, so that nobody touches it. And for the most part, we understand that most people have been paying attention. We did get a chance to speak with many people today who describe it as two minutes of a thunderous noise that they heard streaking across the sky. And many people sharing with us today what they experienced this morning.

(BEGIN VIDEO CLIP)

UNIDENTIFIED MALE: That makes it more real, doesn't it? To actually see pieces of it. Especially here in east Texas, you know, we're not close to a space center or anything.

QUESTION: You feel a little closer now?

UNIDENTIFIED MALE: Yes, I do. We all will for awhile.

UNIDENTIFIED MALE: I saw the tracks after I rushed out of the cafe and saw the streak in the sky that, where an aircraft had come over and we heard the long continuous noise, which didn't sound normal. It sounded like an explosion, and the noise, like thunder, kept in the atmosphere. And then we knew something possibly (ph) happened.

(END VIDEO CLIP)

LAVANDERA: Wolf, just to give you an idea of how difficult this collection process will be, I've spoken already with several residents, who said several hours ago they phoned in reports of small pieces of debris into the authorities here, people would come by and check it out real quick, but it still hasn't been picked up. I imagine that's the case throughout much of east Texas. Some areas are just very remote and very rural areas on some parts. So, it might take sometime just to be able find all of the debris that's scattered over a massive area -- Wolf.

BLITZER: Have you seen, Ed, any of the authorities actually collect the debris? And if you have, how do they do it? Do they have special equipment?

LAVANDERA: We have seen in a couple of places, and also have spoken with residents who saw them pick up the debris as well. They do take good care in terms of figuring out exactly what the situation is and I think it depends on each individual situation where the debris if found as to exactly how they handle it. But of course, they want to be able to preserve everything that's on there. Because, as you know, Wolf, investigators are going count on a lot of this wreckage to perhaps piece this together.

BLITZER: And even one tiny piece of debris could hold the clue to the cause of this explosion. Ed Lavandera, thanks for joining us from Nacogdoches, here in Texas.

Jeff Flock, you have been talking to people here as they gather these makeshift memorials that are going on. A lot of sad folks. JEFF FLOCK, CNN CHICAGO BUREAU CHIEF: I don't doubt we are going to see it all over the country tomorrow, Wolf, but to date this is ground zero. This is where it's happening. This is, of course, where the astronauts live and where they worked.

I want to show us some pictures out at the front gate. It is an incredible scene out there. And I've been to a lot of, I don't know, school shootings, plane wrecks, I have never seen a memorial grow up so rapidly and so large out at the Johnson Space Center main gate.

There are flowers out there. There are balloons. There is an Israeli flag draped out there. All sorts of makeshift memorials. Poems that have already been written by folks that you can tell have just been crafted. It is an incredible scene out there.

And as we said, this is a company town. Yes, it's an oil town, Houston. Yes, it's a cow town. But it's a space town. This is a place where these folks have lived and worked and trained.

BLITZER: OK, we're going to be continuing to talk about what's going on.

Jeff Flock, thanks very much. I know you were here, unfortunately, in 1986 when the Challenger exploded as well. We'll make some comparisons as we go along.

A lot of sad people here at the Johnson Space Center. This investigation, obviously, only beginning, it will last for months, if not years.

Back to you, Miles.

O'BRIEN: All right, Wolf. Thank you very much.

Let's try to put together what we know and give you a sense of where this investigation might be headed. And also give you a sense of some places which might ultimately be some dead ends.

But I'll tell you, what we do know is this: On the launch of the Space Shuttle Columbia, something happened, which caught all of our attention, who watch space shuttle launches.

If you look at this very closely, what you will see here is a piece of the foam, the orange foam on that external tank, fell off at high velocity into the leading edge of the left wing. NASA saw this. Engineers were looking at this throughout the entirety of the six (sic)-day mission, determined after some very careful analysis that number one, they didn't think it cause any truly significant damage. And number two, even if it did, they had zero options to deal with it. And so, the decision was made to let it be.

That was the left wing. The left wing is significant in this, because we do know, that the failure appeared to begin on the left wing based on the telemetry we have heard, from Houston and NASA.

Now, the tiles are a key thing, here. There are some 20,000 of these tiles that coat a space shuttle. And you can see the little bricks here, each of them is absolutely individual, like a little snowflake, if you will, numbered and watched over carefully.

We witness the landing of the Discovery a couple of years ago. And I don't know if you can see, up here, there is a missing tile on the trailing edge of the flap called the elevon. That got a lot of people's attention. One tile missing in a place it was not deemed critical, but it turned out to be a big, fairly serious investigation.

There, you see, that missing tile, there. Why are the tiles important? Well, here's what happens when a shuttle comes back from orbit. I circles the globe a 17,500 miles an hour. It is the perfect equation between speed and a free-fall. And causes it just to free- fall around the Earth. It slows down just enough to begin its fall to Earth.

And as it comes in the atmosphere, it gets into thicker and thicker air. It heats up very quickly. The shuttle's frame is made of aluminum. Aluminum would melt well below the 3,000 degrees, which a space shuttle encounters on that reentry. And so, the space shuttle orbiters are covered with three levels of thermal protection, blankets and tiles, primarily. The black tiles being the ones which are in the position to receive the most heat.

As it comes in, the nose goes high and it begins these steep banking maneuvers, called roll-reversals. All this is about trading speed for heat. Slowing it down and getting it just hot enough to withstand, and at the levels that it can withstand.

The failure, that we witnessed, was just as the space shuttle was at its red hottest, 3,000 degrees Fahrenheit. Those tiles are designed to handle that, but if some of those tiles, a cluster of those tiles, were to fall off, it would -- the shuttle would be unprotected from that tremendous heat.

Now, take a look at this picture. And you will see exactly what was captured as the Shuttle Columbia streaked across the skies of Texas, 100 miles south of Dallas, this morning.

What started off as a single meteor-like streak, which is perfectly normal, quickly turned into something much more ominous as multiple streaks happened as it broke up in mid-flight; at 200,000 feet in altitude, mach 18, much faster than a rifle bullet. We're talking about tremendous velocity. This is the utter apex of the heat and the stresses during this re-entry.

So, if there had been any sort of weakness that occurred in that tile system, whether it happened on launch of it happened for some other reason, this is when it would be come exposed and obvious. And this is exactly what we're seeing here.

Now, there is some concern tonight, the engineers who are pouring over this data, are looking at some unusual movements of those body flaps I was telling you about, those elevons. What that has to do with this? Very early, at this juncture, to draw any sort of conclusions. Now, the debris field is literally a multi-state debris field. There has never been a break up like this in the history of aviation. Something at this altitude, traveling this fast, breaking up into pieces.

And if you look on the left hand side, you are looking at the left-hand side, you are looking at debris, which was recovered from Challenger 17 years ago. The anniversary occurring just last week.

To the right, you see some of the small pieces, which have been strewn across Arizona, New Mexico, Texas, and parts of Louisiana. The question that I have been posing to engineers is the pieces are so small, it is spread over such a large area. Could there be a smoking gun, which would go unnoticed? Which is the harder debris field to handle? One hundred feet below the surface of the ocean, or 100 miles across the state of Texas?

Hard to say, but the fact of the matter is we want to tell you that if you see a piece of the space shuttle, number one, don't touch it for the benefit of your own health. There is a toxic brew on board those space shuttle, mono-methyl (ph) hydrazine, nitrogen tat oxide (ph), nasty stuff. It can cause you all kinds of harm. And certainly, you would not want to grab a souvenir that might be the solution to this terrible and tragic riddle.

Earlier, Wolf Blitzer reported from the Johnson Space Center in Houston. That's home of Mission Control and the pre-flight preparation. Let me tell you just a little bit about the Johnson Space Center. It is sort of the heart and soul of the manned space program. This is where the astronauts live and train. And this is where the simulators are for the space shuttle.

The testing that is done at the Johnson Space Center often sets the standard for future space travels and is the place where astronauts live and work.

Now, working in conjunction with Houston, is the Kennedy Space Center in Florida. It is responsible for the check out, the launch and landing, of course, of space shuttles and their payloads. It is also where equipment designed for the International Space Station gets it final check out. And its preparations before it gets loaded on board the shuttle.

Today, it is were the families of the astronauts had gathered at that shuttle landing facility. That 15,000-foot runway, at the Kennedy Space Center, is where the shuttle returns. The alternate landing site, as you might well recall is Edwards Air Force Base in California.

LOU DOBBS, CNN ANCHOR: Miles, thank you. As you point out, STS- 107 began its journey 16 days ago, launching from Pad A, here at the Kennedy Space Center. The men and women of NASA here today, first shocked, then grief, trying to come to terms with this tragedy. Trying to begin the process here, as in every NASA center across the country, of trying to understand what had caused the loss of life, the loss of the Columbia.

But the first thing that the men and women of NASA today wanted to do was remember, to honor, and to pay tribute to the seven crew members lost this morning on the Columbia. And NASA observed a minute of silence.

(BEGIN VIDEO CLIP)

UNIDENTIFIED MALE: Well, I'm feeling pretty bad about this, actually. Ever since Challenger crashed, I thought there was never going to be another space shuttle accident. Now, I'm here today. At the memorial, I'm ashamed (ph) of the seven astronauts that were killed at this time today. That's all I have to say.

UNIDENTIFIED FEMALE: It's just pure shock. Disbelief, this is unreal. I mean, you come out here expecting to see a shuttle land and it is just not there. It's just not there. It just completely floors you.

UNIDENTIFIED MALE: It is sort of heart rendering, because of the loss of these people. And it is hard to even conceive that we've lost additional people.

(END VIDEO CLIP)

DOBBS: John Zarrella has been here with me throughout much of this tragic day. And John, these fallen astronauts who we honor and remember tonight, not alone (ph), as the tragic victims of the failures of amidst all of the glorious successes of the U.S. space program.

JOHN ZARRELLA, CNN CORRESPONDENT: That's right, Lou. As a matter of fact, as you are well aware of, not too far from here at the visitor's center there is a memorial to the astronauts. That granite slab over there, and lots of people here today, because they expected to see a landing.

Always busy on weekends, more so today, they did not see that landing and when word filtered down, and finally came out that in fact there had been a terrible tragedy over Texas, many people began to go to that granite memorial. It is a wall and inscribed on that wall the name of 17 astronauts who have perished. Of course, the Challenger VII, the Apollo I fire victims, the three astronauts there. And then another seven astronauts who perished in other means, who had not made it to flight.

So, 17 astronauts in all, people went to pay their tributes there. What they did was to lay flowers, some of them prayed, some of them just observed a moment of silence as the NASA workers themselves did as well.

And we can certainly expect that, as we saw out at the Johnson Space Center, that the memorials, the ad lib memorials that people are bringing, will probably grow and grow as the days go by her at the Kennedy Space Center, as people come to pay tribute, tragically, once again, to seven more fallen heroes.

DOBBS: To pay tribute and to come to terms with grief.

John, thank you very much. John Zarrella.

Now, back to you, Miles O'Brien.

O'BRIEN: Thank you very much, Lou.

One of the astronauts who has flown on Columbia, as a matter of fact, one of the most seasoned astronauts ever, NASA's Story Musgrave will be with us shortly. I'll talk about Columbia with him, and the risks and rewards of space flight after we take a brief break. Stay with us.

(COMMERCIAL BREAK)

O'BRIEN: We'll have more on this in just a moment. And we're going to be hearing from Story Musgrave, six-time shuttle flyer, retired in 1996 from NASA. His insights will undoubtedly be helpful to us all on this tragic day.

But before we do that, let's go back to Houston and Wolf Blitzer -- Wolf.

BLITZER: Thank you very much, Miles.

A lot of people are focusing their attention right now on these seven astronauts. Who exactly were they? We know that over the past several years they've been training very intensely, here in Houston at the Johnson Space Center. But all of these seven individuals were remarkable. Here is CNN's Frederick Whitfield with a look at the seven.

(BEGIN VIDEOTAPE)

FREDRICKA WHITFIELD, CNN CORRESPONDENT (voice-over): Shuttle Commander Rick Husband never had any question about his chosen profession. He knew since childhood, he wanted to be an astronaut.

RICK HUSBAND, COMMANDER, SPACE SHUTTLE COLUMBIA: Well, from the time that I was about four years old I wanted to be an astronaut. And it was about that time when the Mercury program started up. And so I saw those things on the TV. And it just really excited me.

WHITFIELD: He joined the Air Force, became a test pilot, rose to colonel. And in 1994 joined the NASA and achieved his goal. Five years later Husband piloted the Shuttle Discovery on the first docking with the International Space Station.

Rick Husband was married, with two children.

Payload Specialist Ilan Ramon, the first Israeli in space, leaves behind a wife and four children. Ramon served as a fighter pilot before being chosen as his nation's first astronaut in 1997.

Indian-born Mission Specialist Kalpana Chawla, earned a degree a degree in aeronautical engineering in her home country before moving to the United States, where she became a citizen and joined NASA. Chawla made her inaugural space flight in 1997.

For Pilot William McCool the Columbia mission was his first flight into space. A former test pilot, he was responsible for maneuvering the shuttle during its numerous scientific experiments.

Air Force Lieutenant Commander Michael Anderson was Columbia's payload commander. Married with two children, Anderson was the son of an Air Force pilot, raised around military bases. He had been in space once before on a 1998 shuttle flight that delivered equipment to the Russian Space Station Mir.

Anderson was in charge of the shuttle's science experiments and said he was energized by the potential for discovery.

MICHAEL ANDERSON, PAYLOAD COMMANDER, SPACE SHUTTLE COLUMBIA: Yes, I am excited about this flight. This is a really exciting flight. I think if you take each of the payloads that we have on this flight, and you sit down, and you really look at it, and you really study them, you realize that there is tremendous potential.

WHITFIELD: Mission Specialist David Brown was a U.S. Navy captain, a pilot, and a flight surgeon. He became an astronaut in 1996 and was making his first trip into space. Although his focus was on specialized experiments, Brown recognized the broad appeal of space exploration.

DAVID BROWN, MISSION SPECIALIST, SPACE SHUTTLE COLUMBIA: While the dream of going to space is not unique to just astronauts or Americans, or any particular nationality, it is a broadly held dream. So the fact that other countries and other people want to do that is no surprise.

WHITFIELD: Columbia's other mission specialist was Laurel Clark, a U.S. Navy commander and a flight surgeon. She was aboard submarines after medical school, before becoming an astronaut.

Dr. Clark spoke from the shuttle just hours before the Columbia lost communications with NASA ground controllers.

LAUREL CLARK, MISSION SPECIALIST, SPACE SHUTTLE COLUMBIA: Good morning, Houston. We are getting ready for a big day up here. Had a great time on orbit and really excited to come back home.

WHITFIELD: Laurel Clark leaves behind an eight-year-old son.

Fredricka Whitfield, CNN.

(END VIDEOTAPE)

BLITZER: Family members are understandably reluctant to speak out so quickly after this horrible tragedy, although some are actually seeking to make their views known. Here's some of the reactions from some of the loved ones.

(BEGIN VIDEO CLIP)

ELIEZAR WOLFENMAN, ILAN RAMON'S FATHER: I can't believe it's happened. He was -- I was so happy for him. I got his e-mail, it was the top of his life, and that's what happened.

I had a connection with him in e-mail. Yes, and just two days ago I got the last e-mail from him. And he was so happy. And he said that he was so happy that he doesn't want to come to Earth.

And he didn't come back to earth.

JOHN SALTON, BROTHER OF LAUREL CLARK: There was complete panic at the moment I realized that there was something -- something had gone wrong. I was -- I had the TV on in here and the computer on in the other room. And I was running in between trying to find out what was going on. I was -- it was awful.

(END VIDEO CLIP)

BLITZER: A church services throughout this area, in Houston, especially around the Johnson Space Center the grief will be very, very visible during the services Sunday morning -- Miles.

O'BRIEN: Wolf Blitzer, in Houston, we'll check in with you in just a few moments.

And we will be checking in with Story Musgrave, six-time shuttle veteran, first flew in 1983, last flew in 1996. Quite a storied career, if you will excuse that expression. Stay with us for that, after a brief break.

(COMMERCIAL BREAK)

O'BRIEN: Welcome back to our special report on the tragedy of the space shuttle "Columbia."

We're going to be talking to Story Musgrave in just a moment.

Before we do that, let's get an update on the latest facts as we know them, from Anderson Cooper -- Anderson.

COOPER: Miles, thanks very much.

We can report that human remains have been recovered from the debris field in Hemphill, Texas. Authorities are assuming they may be that of a Columbia crew member. Shuttle debris is being found in yards, fields, and various other places throughout the state. People are being cautioned against touching whatever they might find because it might be toxic.

In honor of the Columbia crew, President Bush today ordered flags on all federal buildings to be flown at half-staff until Wednesday. The governors of many states have done the same.

We're now going to take -- check in -- actually, we'll just go back to Miles O'Brien -- Miles.

O'BRIEN: All right, Anderson, thank you very much.

You know, one of the reasons we explore space is to push the boundaries of science. And for the shuttle "Columbia," the 16 days in space had been completely earmarked for scientific experiments. Not an exaggeration to say that years and years of effort went into getting these scientific experiments together, and, in this case, to fly on this particularly long science mission.

The Columbia carried experiments on changes in the spread of flame in space. Flames do not burn like they do here in the world of gravity, an important thing to know when you have an ongoing International Space Station.

Also, flowers that grow in space don't smell the same. Why? Well, we don't know. That was one of the experiments. The effects of weightlessness on rats and how that might relate to human beings who spend long-term stays in space. Measurements of atmospheric dust, this was the prime experiment for Ilan Ramon, the Israeli astronaut. He was looking at how dust might have something to do with global warming, particularly looking at dust storms in the Middle East.

And bee and spider behavior in weightlessness was also looked at, all in the quest for learning more about the human body performs and in some cases doesn't perform in the absence of gravity.

All that with an eye toward further exploration one day in space.

Now, more than one former astronaut was probably reliving a mission or two before today's events went horribly wrong.

With us is Story Musgrave, a veteran of six space flights, and Mae Jemison, the first African-American woman to fly in space, who flew one mission in 1992.

I want to begin with you, Story. You had the opportunity on your last mission to make some observations about reentry and the heat that is encountered when a shuttle reenters the atmosphere. Tell us a little bit about what you saw and what impressed you about it.

STORY MUSGRAVE, SIX SPACE FLIGHTS: Yes, Miles, I think heat rejection is a critical factor in what happened today, and to get a real feel for how much heat you need to reject, if you look at a launch, the external tank, how much fuel, the solids, with how much fuel, all of that energy that goes into a launch has to come out on the heat of reentry.

And so if you look at burning up the amount of fuel that is carried, it has to come out in the heat of reentry.

On S.T.S. 80, my final flight in 1986, after an 18-day flight, I had no responsibility, no technical responsibility during the entry. So I had the opportunity to simply stand with all my gear on in the flight deck and look out the overhead window. So from your point of view, if you'll have the nose going that way, the tail toward you, and I am here looking out the overhead window, from Mach about 23 down to Mach 10, the amount of fire that you are engulfed in, you cannot believe that you are not evaporated in a flash.

But what is amazing is, you are absolutely enveloped in this flame, but the flame paints your shock waves. And so the flame is a medium, and you see the supersonic shock waves in there. You see this blue lightning coming off the nose that is energizing this whole pattern.

Whenever a rocket jet, an attitude control jet goes off, the whole thing dissipates, and it comes back in a flash.

O'BRIEN: Wow, right.

MUSGRAVE: And I did, standing up, I was able to hold a camcorder in the window and record that and show my fellow crew members with a little monitor.

What was amazing, in S-turns for navigation, and to manage our energy, in those S-turns, on one side of the tail I had a different auroral color, and on the other side, I would have a different color.

O'BRIEN: That's fascinating.

MUSGRAVE: And this was really amazing to me.

O'BRIEN: When you witnessed that, you had to be impressed with how much work these tiles have to do, these little tiles, little teeny pieces laid together like bricks, which are very fragile, and yet really hold your lives in their hands, if you'll excuse that -- giving it personification. But nevertheless, it's a fragile system and yet a hardy system, isn't it?

MUSGRAVE: I would call it a fragile system. I'd call it a very critically vulnerable system in which everything has to come out perfectly. I look upon launch as a beautiful butterfly that's bolted on a bullet. But today, of course, the emphasis is on reentry, and how tens of thousands of tiles have got to do their thing.

O'BRIEN: Let's go to Mae Jemison. Mae, you flew in 1992, and did you have a similar experience on reentry? Did you have this sense of being enveloped in tremendous heat?

DR. MAE JEMISON, SPACE PIONEER: Well, what Story described really talked about looking at -- looking out the window. When you're actually seated, you don't have that sensation. Basically what you're feeling is that all of a sudden you're getting weight again, you've been in space for a number of days. The members of the crew who are on the flight deck are watching the computers, watching what's going on to try to make sure that nothing is going awry.

But you don't actually have that feeling, because you're not seeing it, which is what's remarkable about what Story was able to observe. I think...

O'BRIEN: It seems like a wild ride, Mae. Is it?

JEMISON: Coming back in?

O'BRIEN: Yes.

JEMISON: It doesn't -- no, you're going -- you're bleeding off a lot of energy. But what's going on inside of the shuttle, I didn't feel like it was a very wild ride. In fact, it was fairly tame from what you expect.

But I think that the comment you made about the tiles is very true. The tiles do an incredible amount of work, because they have to insulate the shuttle in a very small distance of space. And they've done that task many times.

O'BRIEN: Story, let's go back to what you were saying about it being a fragile system. In a way, I think a lot of people would say, Wait a minute, fragile? It's coming in at beginning at Mach 25, slowing down to zero, ultimately, at the runway, shedding off heat all the while, entering the atmosphere under tremendous stress. Surely it has to be a hardy system.

MUSGRAVE: No, sir, I don't look upon it as a hardy system. The engineering has to be perfect, and the engineering has been perfect. It's a marvel that the system has been able to pull it off. I still call it a very, very fragile system. A tile is like this, a tile is about this thick, but it weighs nothing, and you can feel it, even when it's almost white-hot, because it has no heat capacity. You can push your finger right into it.

All of that has to work. You can have Mach erosion, in which your supersonic -- you can have Mach erosion that can eat you, eat you into pieces.

O'BRIEN: Story...

MUSGRAVE: There's all kinds of very high-tech engineering involved.

O'BRIEN: All right, I'm curious that you...

JEMISON: But I would like...

O'BRIEN: Go ahead, Mae, go ahead.

JEMISON: ... a comment in the terms...

O'BRIEN: Please do.

JEMISON: ... when you talk about fragile. I would think of many times when you talk about systems as fragile, if you talk about the human body as fragile, if you find the right -- if the right problem, the right accident comes along, then something that seems relatively minor can be catastrophic. But at the same time, the human body is remarkable. I think if you look at it as fragile in that sense, then you get a better feel for what Story is describing, that it does this -- it has this tremendous precision engineering that has worked over and over again. But if you get to a point where you have the right accident, then something catastrophic can occur.

O'BRIEN: That's an interesting analogy, I hadn't heard it put that way, but that seems to make a lot of sense to me.

Story Musgrave, we've been talking a lot about that piece of foam which fell off the shuttle on ascent not long after liftoff, struck the left wing. NASA looked at it, didn't determine that there was anything really serious there, or that was the conclusion, at least, at the time.

Do you think that that is ultimately going to be a dead end, or is that something that ultimately will lead to some sort of conclusion as to what went wrong?

MUSGRAVE: I'm sorry, Miles, I just don't have the technical information. I just don't know what to say on that one.

O'BRIEN: All right. Well, we appreciate your being honest and candid and not getting into the realm of speculation.

JEMISON: I think that definitely an answer will be found, and I have a feeling that it'll be found very quickly, because you remember the shuttle has an incredible amount of data and telemetry that's coming down constantly. And an answer will be found.

We'll figure out how to fix some parts of it. You can't say that every phase of human space flight is always going to be survivable, nor can we make it survivable. But how we move on with the space program is really going to depend on the commitment of the American public and how we react to this.

I remark that when I was a little girl and the Apollo I fire occurred, we found out what happened, and we said, Let's go to the moon. And I think that's what we need to do now, is to really find out what happened, fix what we can to the best of our ability, but don't say that we can't do this, we can't explore space, we can't expand human presence...

O'BRIEN: Story...

JEMISON: ... until we make it completely, completely without any problems.

O'BRIEN: Story, you became an astronaut in 1967 and lived through all that. Just briefly, as we take away from that, having that experience, Apollo I, "Challenger," and looking at this from afar, do you have any doubt in your mind that the U.S. will return to space with human beings inside spaceships?

MUSGRAVE: Miles, I have no doubt at all. We have to go forward for lots of reasons. We will have other accidents. They're unavoidable. Even since "Challenger," I'm incredibly proud of this team. I have seen nothing but the right kinds of decisions, the right kind of actions, the right kind of tender, loving care. I mean, really explicit care. I'm incredibly proud of this team.

But we are going to have more accidents. But I think what we have to have is a vision for where we are going into the future. We have no vision for what vehicle is to come next. We have no ideas about what we might do next, not only in terms of human space flight, but also robotic missions to explore the planets, the moons of the planets.

In other words, where would we like to be 10 years from now, 15 years from now? We have to think ahead, and we just have to keep pushing forward. We need to get a low-cost, reliable access to space and things like that, and we need to blend the robotic missions with the human missions so we can optimize our pursuit of space flight.

O'BRIEN: Story Musgrave, shuttle veteran, six flights. Mae Jemison, first African-American woman to fly in space. Thank you both for being with us tonight on this special report on the tragedy of the space shuttle "Columbia."

We will take a break. When we return, we'll look at the issue of the aging shuttle fleet. A lot of people would tell you that's a misnomer. The shuttle's airframes, designed for 100 missions. This was the 28th mission of the space shuttle "Columbia," although it was more than 20 years old. Question is, were they old, or were they made new every time around?

Stay with us.

(COMMERCIAL BREAK)

O'BRIEN: When the space shuttles were designed in the mid-'70s, it was thought they would fly much more frequently. Each of them was designed to fly 100 missions. This was Columbia's 28th mission, and the 113th mission in the space shuttle history so far.

The question is, are they too old to be flying? Some have brought those questions out. But anybody who's spent any time looking at space shuttles and how they're treated, to say they least, they are babied.

(BEGIN VIDEOTAPE)

O'BRIEN (voice-over): Something old is nothing new for NASA's manned space flight effort, dealing with a spacecraft designed in the '70s and launch facilities built during the moon race.

The first sign of trouble came here, deep in the tangle of wires and pipes inside the aft compartment of "Atlantis" in June. An eagle- eyed inspector saw this, a crack no bigger than a third of an inch, a small thing, but in a critical spot, the 12-inch pipe that carries liquid hydrogen rocket fuel from the shuttle's big external tank to its main engines.

UNIDENTIFIED MALE: The worst-case scenario is that you could continue to crack, break off a piece of the material. But if that material breaks off and gets ingested by the main engine, it could be a bad day, it could be a catastrophic event for us.

O'BRIEN: More inspections ordered, more cracks found, about a dozen in all. The fleet was grounded, and Dittemore called for the aerospace equivalent of a full court press led by chief engineer Ralph Rowe (ph). He has the briefing charts to prove it.

UNIDENTIFIED MALE: We were working 300 actions in parallel, so we had a team structured to handle a workforce of 200 and 300 action items, and we were meeting on a daily basis until we got a decent handle on what the problem was.

O'BRIEN: They now believe it was a flaw in the way the pipes were made a quarter-century ago. But simply ordering new parts from the manufacturer was not a viable option.

UNIDENTIFIED MALE: The jigs and the tooling and even some of the people are now gone away. We have now been in contact with them, and they are pulling the tooling out to go manufacture some additional lines. And they're also pulling back what we call some of the graybeards that understand how you go build those lines.

O'BRIEN: So instead, the cracks were welded over and polished smooth by the steadiest hands in the hangar.

UNIDENTIFIED MALE: We're not going to fly with something we don't understand. So we are going to take a time out.

O'BRIEN: The shuttle team will likely push for continued improvements to the avionics, hardier wheels and tires, replacement of old tape data recorders with digital technology, even replacing clunky old circuit boards.

UNIDENTIFIED MALE: You cannot replace this vehicle with the exact capabilities that we have and be cost-effective at it.

O'BRIEN: But in the space business, even the first step can be daunting. While engineers burned the midnight oil to fix the fuel line cracks, another team found some badly cracked bearings in the 37- year-old crawler that takes a stacked shuttle out to the pad.

Miles O'Brien, CNN, Houston.

(END VIDEOTAPE)

O'BRIEN: And that report came several months ago. The issue of those cracks in the fuel lines unlikely to have anything to do with this. But the general issue of age and fatigue in metal is an issue that will be looked at.

Randy Avera is a veteran of the Challenger investigation. He's been with us all day helping us understand some of the technicalities.

To what extent do you think, Randy, that the possibility of age or metal fatigue might come into play here?

RANDY AVERA, FAA INVESTIGATOR: Well, the key here is reliability. Reliability is a factor that directly affects safety. And age always is a factor in reliability. Design and age cycles, maintenance program, all that comes down to the reliability. The original vision of the shuttle program was a 10-year program, each orbiter designed for 100 missions with a two-week turnaround.

Course, we all know that's not the actual track record of the time and frequency of flight of the shuttle.

O'BRIEN: Not even close, as a matter of fact. The turnaround appeared -- well, it turned out to be much more complicated.

Let's talk then about something that struck me about that piece and something that Ron Dittemore said, which stands in stark contrast to the days before "Challenger," which is, those cracks were found, and they called a time out. They've had a lot of time outs of late. There was a problem with the wiring a couple of summers ago, grounded the entire fleet to look at several nicks in wires all throughout the fleet of four at the time.

It seems as if there had been a sea change in the way NASA thought after "Challenger." Would you agree?

AVERA: Well, the whole purpose of the "Challenger" investigation in 1986 was to find a new way of doing business in regard to quality and accountability of management. And that the problems found at the lowest working levels would find their way reliably and accurately to the management staff for proper review and decision for safety of launch questions.

In regard to the design, we're talking about a design that's from the 1960s, and it's clearly time that the United States and other countries cooperate in looking to the future, in looking to new designs and ways of coming up with the funding for that, and expanding the fleet of orbiters from four to a fleet that is of a useful size for the near-term and long-term future.

O'BRIEN: All right, but Randy, do you think, in your heart of hearts, that NASA has been flying the shuttle safely post- "Challenger"?

AVERA: I can say from being an investigator that NASA on a regular working basis has tremendous technical problems that are just amazing that are accomplished. And as far -- we're talking human beings here. NASA does what is humanly possible to address this.

And what I would refer to as the NASA method, it's the method which has been developed by NASA over the last 40 or so years in the national aerospace organizations prior to that, like NACA (ph), for example, that was prior to NASA. The NASA method is about quality control and precision and skill in manufacturing and training. And people are human. There's a limit to what we can expect humans to accomplish.

O'BRIEN: Randy Avera, thanks for all your efforts on our behalf today, and we will be checking in with you as this investigation unfolds.

From the start, when the president heard that NASA had lost contact with the shuttle Columbia, Mr. Bush feared the worst.

CNN's Suzanne Malveaux visits the Situation Room on this somber day.

(BEGIN VIDEOTAPE)

SUZANNE MALVEAUX, CNN WHITE HOUSE CORRESPONDENT (voice-over): In honor of those lost, the flag at the White House lowered at half- staff. President Bush once again charged with carrying out the somber duty of bringing the nation together in time of tragedy.

GEORGE W. BUSH, PRESIDENT OF THE UNITED STATES: My fellow Americans, this day has brought terrible news and great sadness to our country. At 9:00 this morning, Mission Control in Houston lost contact with our space shuttle "Columbia." A short time later, debris was seen falling from the skies above Texas. The Columbia is lost. There are no survivors.

MALVEAUX: Six Americans and one Israeli lost, people the president said assumed great risk in the service to all humanity.

BUSH: The cause in which they died will continue. Mankind is led into the darkness beyond our world by the inspiration of discovery and the longing to understand.

Our journey into space will go on.

MALVEAUX: Just after 9:00 this morning at Camp David, President Bush is notified by his chief of staff that NASA has lost contact with the shuttle. At 10:30, he is briefed by NASA's director and decides to return to the White House early.

The Situation Room at the White House goes into full gear, notifying all the principals. By 12:30, the president is back in the Oval Office, when NASA's director tells him there are no survivors.

Fifteen minutes later, Mr. Bush, standing at his desk, holds a conference all with the victims' families, who are gathered around a speakerphone at the Kennedy Space Center. He tells them, "We express our love and appreciation for all those who died today. I want the loved ones to know there are millions of Americans praying for you, including me and Laura. It's an incredibly tough day for you. May God bless you all. I wish I was there to hug, cry, and comfort you right now." In a poignant moment, a White House aide who was with the president says after the call, a somber Mr. Bush briefly excused himself to the executive residence.

The president also called Israeli Prime Minister Ariel Sharon to offer his condolences for the Israeli astronaut lost, and the president received calls from world leaders, from Mexico, Canada, and even those recently at odds with the president over his stand with Iraq, France and Russia.

(on camera): It was a big test for the Department of Homeland Security, its new secretary, Governor Tom Ridge, able to collect and assess information quickly, to assign FEMA the lead role in recovery, and to reassure the American people that no matter how tragic this disaster was, it was not the result of terrorism.

Suzanne Malveaux, CNN, the White House.

(END VIDEOTAPE)

O'BRIEN: It's been an emotional day for all of us here at CNN, for all of us in this country.

I'm Miles O'Brien. Thank you for being with us.

To close out this hour, we thought we'd take you back to earlier in the Columbia mission with words and pictures from high above the earth, happier times.

(BEGIN VIDEO AND AUDIO CLIPS)

UNIDENTIFIED MALE: ... three, two, one. We have booster ignition and liftoff of space shuttle Columbia with a multitude of national and international space research experiments.

UNIDENTIFIED MALE: From the time I was about 4 years old, I wanted to be an astronaut.

UNIDENTIFIED MALE: I couldn't be any more excited about a space mission than I am about this one.

UNIDENTIFIED MALE: It's beyond imagination until you actually get up and see it and experience it and feel it.

UNIDENTIFIED FEMALE: Good morning, Houston. We're getting ready for a big day up here, had a great time on orbit, and we're really excited to come back home.

UNIDENTIFIED MALE: And "Columbia," Houston. We see your tire pressure messages, and we did not copy your last.

UNIDENTIFIED MALE: Roger...

BUSH: This day has brought terrible news and great sadness to our country. At 9:00 this morning, Mission Control in Houston lost contact with our space shuttle Columbia. The Columbia is lost. There are no survivors.

UNIDENTIFIED MALE: This is indeed a tragic day for the NASA family, for the families of the astronauts who flew on S.T.S. 107, and likewise tragic for the nation.

UNIDENTIFIED FEMALE: Pure shock. Disbelief. This is unreal. I mean, you're- you come out here expecting to see a shuttle land, it's just not there.

UNIDENTIFIED MALE: I'm crying because seven people got (UNINTELLIGIBLE) got lost in this.

UNIDENTIFIED MALE: We're devastated because of the events that unfolded this morning. There's a certain amount of shock in our system because we have suffered the loss of seven family members. But our thoughts and our prayers go out to the families of Rick and Willie and David and Kalpana, Michael, Laurel, and Ilan, true heroes. And we are suffering for the events that have happened this morning.

UNIDENTIFIED MALE: She'd been working towards that goal of getting up there, and I'm thankful she at least got to do that. And I just wish I could have had a chance to actually hear back from her what it was like. And I'm going to miss her.

UNIDENTIFIED MALE: We are a nation of explorers. We have always -- that's why this great nation has come to what it is, and the space program will go on too for that reason.

BUSH: These astronauts knew the dangers, and they faced them willingly, knowing they had a high and noble purpose in life. Because of their courage and daring and idealism, we will miss them all the more.

(END VIDEO AND AUDIO CLIPS)

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